The invention relates to a liquid fuel dispensing system as may be used, for example, at a road-side petrol filling station. In particular, the invention relates to a system comprising a plurality of dispensing pumps controlled by a central control where payment may be made. Generally, the pumps will be of the self-service kind where the customer himself dispenses the fuel.
In such centralized control systems, it is necessary to transmit data to the central control from each pump representative of the quantity and perhaps the value of fuel dispensed. Also, in systems where it is possible for the customer to select one of a number of grades of fuel, it is necessary to transmit information concerning the grade selected. It has been proposed to equip the fuel meter at the pump with an electric pulse transmitter which transmits a pulse to the central control as each unit volume of fuel is dispensed. The pulses are received at the central control where they are counted and calculation is made to determine the cost of the transaction. Such systems suffer from the disadvantage that electrical interference picked up on the data transmission lines between the pumps and the central control can be interpreted as volume or money pulses and give a faulty indication at the central control. The present invention seeks to provide a system in which this disadvantage is alleviated.
According to the present invention, there is provided a liquid fuel dispensing system comprising a plurality of liquid fuel dispensing pumps each having a fuel meter, an electric pulse transmitter associated with the fuel meter of each pump to generate pulses representative of the volume of fuel dispensed, a central control, a data transmission link between each pump and the central control whereby information may be transmitted from the pump to the central control representative of the volume of fuel dispensed, a pulse store at each pump which accumulates pulses transmitted by the associated pulse transmitter in a dispensing operation, and sampling means at the central control which repetitively samples the outputs from the pulse stores to derive inputs representatives of the volumes dispensed, which inputs are updated at each sampling. With this arrangement interference on the data transmission link received while a sample is being taken may upset the input to the central control. However, the error will be rectified in subsequent sampling. As a special feature of the invention, means are provided to release a given pump to a second customer while storing the information from the previous transaction.
While it is envisaged that this system may be applied where the data links are individual pairs of transmission lines between the central control and respective pumps, further benefits are achieved by use of a multiplex transmission system over a single data path. The multiplex system may be frequency multiplex but is preferably time-division multiplex. With individual transmission paths for the pumps or with frequency division multiplex, it is possible to effect sampling of the different stores simultaneously in a parallel manner. However, it is preferred, and with time-division multiplex is necessary, to effect sampling cyclically in a serial manner. Thus, in a preferred embodiment of the invention, the data transmission links comprise a common data path, time-division multiplex means are provided, the sampling means comprises an interrogator which cyclically interrogates the pump pulse stores and the pump pulse stores have associated responders which respond on being identified in the interrogation to transmit information from the pulse store to the central control.
The use of a single transmission link allows the system to be installed with the minimum of physical disturbance and cost, since the lines coupling the pumps to the central control may need to be laid in the concrete floor of the station. Even greater benefit is achieved if, as is preferred, the common transmission link is constituted by the power lines which provide electric current for the pump motors. Data transmission over the power lines is effected by a high frequency carrier which is modulated by the data signals and demodulated at the central control. The main supply system may be a ring main system or it may be a star system in which the supply lines for the pumps radiate from a common point. It is to be understood that the use of a star system does not detract from the concept that the data link is common to all the pumps, being the star main system in this case.
The system described thus far is applicable to pumps of a simple single-grade kind. Such pumps are in use at the present time, but there is a tendency to replace them by blending pumps which blend two base grades of fuel together in a ratio chosen by the customer to give a preselected grade of fuel. However, it is a feature of the present invention that the system is compatible with single grade pumps and blending pumps. The single grade has a mechanical drive for driving indicator drums representative of volume of fuel dispensed and the total cost of the fuel dispensed. It is proposed with such a pump to drive the pulse transmitter from the drive for the cost drum and to provide a pulse store for those pulses, the accumulated cost total, which is representative of volume, being transmitted to the central control. At the central control, a calculator is provided to derive a representation of volume dispensed from the cost information from the pump. The calculator is pre-set with the unit price of the grade concerned.
Apart from the foregoing example of a mechanical single-grade pump, it is preferred that the system should be such that volume and cost calculations, as well as information storage, should be effected at the pump instead of at the central control. This allows the pumps a degree of independence of the central control so that in the event of failure of some part of the central control, the pumps may be operated conventionally. Also, in the event of failure of part of the calculating equipment, only the pump concerned is affected and the remainder of the system can continue to be used.
The system is applicable to mechanical blending pumps in which blending control is effected by a mechanical differential responsive to any discrepancy from a pre-set value of the ratio of movement of two meters in the respective fuel lines. However, the system is also applicable to a blending pump in which blending control is effected in response to an electrical error signal.
Preferably the pulse store at the pump comprises a recirculating shift register which carries the totals of pulses representative of volume dispensed and cost.
The provision of volume and cost indication in updated digital form conveniently allows the use of an electronic digital display at the pump. The display may employ seven-segment digital indicators mounted on the body of the pump. Additionally, or instead, a similar display may be arranged on the dispensing nozzle itself. A system for monitoring the display to detect faulty segments is proposed.
It is necessary for the current unit price of fuel to be displayed. Also, it is desirable to be able to change the current unit price quickly at will, perhaps adjusting the price in accordance with the time of day, for example. In order to do this, a unit price display at the pump can be arranged to be controlled by signals from the central control and the displayed information can be updated in every cycle of the repetitive sampling scan.
Provision is made for interfacing the system with a wide range of peripheral units. The general philosophy is that all the pump data is available on the data path, and that any peripheral unit which needs this data can obtain it through an adaptor unit connected to the data path. Specific consideration has been given to the use of note readers, cash registers, trading stamp issuers, printers and credit card acceptors, but since all of the system invention is available in the central unit, any peripheral unit which requires this information could be accommodated.